The present invention relates to a method and an apparatus for controlling a copier, facsimile apparatus, printer or similar image forming machine and, more particularly, to a method and an apparatus for adjusting a process condition for image formation on the basis of a sensed control parameter particular to image formation.
A conventional control method for the above application senses a control parameter particular to image formation, e.g., the surface potential of a latent image electrostatically formed on an image carrier (light portion or dark portion) and adjusts, based on the sensed surface potential, a charging condition, exposing condition or similar process condition for image formation. With this method, it is possible to stabilize the surface potential of the image carrier at a target value. For this kind of scheme, a reference may be made to Japanese Patent Laid-Open Publication Nos. 64-78268, 2-52368, and 3-136072 by way of example.
The conventional process condition control method has some problems left unsolved, as follows. Assume that a change in the surface potential or similar control parameter is increased for a minimum control amount of the process condition. i.e., a control resolution is lowered. Then, although a period of time necessary for the actual surface potential to approach a target potential, i.e., a control time may be reduced, the degree to which the surface potential is close to the target potential after the control. i.e., control accuracy is lowered. While a smaller change in the surface potential for the minimum control amount, i.e., a higher control resolution will enhance the control accuracy, it increases the control time. For example, a target value for control is provided with a relatively narrow tolerance width in order to enhance the control accuracy. Then, a high control resolution is required for preventing the surface potential, or control parameter, from failing to converge due to jitter when the control amount of the process condition is shifted up or shifted down in the vicinity of the target value. The high control resolution results in a long control time, as stated above.